Circuit-breaker having dielectric liquid under pressure

ABSTRACT

A circuit-breaker includes a fluid-tight cutout chamber in which are disposed a fixed contact as well as a sliding movable contact and which encloses a dielectric in the liquid state kept under pressure. The movable contact is brought and kept selectively against the fixed contact by releasable disconnecting means, in opposition to ever-present elastic disconnecting means tending to separate the two contacts and comprising hydraulic elastic means responding only to the volumetric elasticity of the compressed liquid in the circuit-breaker. The dielectric in the liquid state is preferably a compressible liquid having a compressibility at least ten times greater than that of oil and may be a liquified gas dielectric.

[ Oct. 15,1974

United States Patent [1 1 Gratzmuller CIRCUIT-BREAKER HAVING DIELECTRICAttorney, Agent, or FirmHolman & Stem [57] ABSTRACT A circuit-breakerincludes a fluid-tight cutout cham- Jean Louis Gratzmuller, 66 Blvd.Maurice Barres, 92 Neuilly sur Seine, France Oct. 2, 1972 [22] Filed:

her in which are disposed a fixed contact as well as a pp 294,291sliding movable contact and which encloses a dielectric in the liquidstate kept under pressure. The mov- [30] Foreign A li ti p i i Data ablecontact is brought and kept selectively against the fixed contact byreleasable disconnecting means, in

opposition to ever-present elastic disconnecting means tending toseparate the two contacts and comprising hydraulic elastic meansresponding only to the volumetric elasticity of the compressed liquid inthe circuit-breaker. The dielectric in the liquid state is preferably acompressible liquid having a compressibility at least ten times greaterthan that of oil and may be a liquified gas dielectric.

W GQR M N 3 M35 1 9 M8 m 4 S m A W T w WA m m H m 0 m n O "H P m 2 0 C 0S n R m2 m 0 a CT n 5 mm mA m n u rT F 0 m RS 0 h eD l 2 R m In T I "mamI 3 C00 U L .M w Smh S UIF 2 8 6 555 5 [rlft r...

200/148 0 Gratzmuller.................... 200 150 A 10 Clams, 2 DrawingFlgllres 3,406,269 10/1968 Fischer............ 3,569,651 3/1971CIRCUIT-BREAKER HAVING DIELECTRIC LIQUID UNDER PRESSURE This inventionrelates to electrical circuit-breakers in which at least the cutoffchamber, which encloses the fixed and movable contacts, is filled with adielectric liquid kept permanently under pressure.

Circuit-breakers of this kind have already been described in French Pat.No. 1,537,673 filed on April 15, 1966 by the same inventor. It will besufficient to recall here that the act of bringing about the cutting offof the current, by separation of fixed and movable contacts, in adielectric medium constituted by a liquid kept permanently underpressure allows certain electrical characteristics of the dielectricmedium to be improved (for example disruptive strength, extinguishingpower). In this way there can be obtained better cutoff performancesand/or a reduction of the volume of dielectric (especially due to thereduction of the separation necessary between the two contacts whendisconnected), and thus a reduction in bulk and cost of the apparatus.

Such circuit-breakers with dielectric liquid under pressure areparticularly advantageous when there is used as the dielectric liquid aliquified dielectric gas, kept under pressure to remain permanently inthe liquid state, such as sulphurhexafluoride.

Finally, in such circuit-breakers, there is provided elastic means formaintaining the dielectric liquid under pressure (for example pneumaticelastic means constituted by a cushion of gas under pressure) and thissame elastic means, at all times available, being utilised to set themovable contact of the circuit-breaker in motion in the directionseparating the contacts, i.e., for the disconnection.

In practice, the cutoff chamber has been in communication with a reserveof dielectric liquid under pressure constituted by a hydropneumatic orhydromechanical accumulator, communication between the cutoff chamberand the accumulator being ensured by passages or conduits which areshort and/or of ample section to permit the exchanges of liquid withoutdelaying the time of the connecting or disconnecting operations. Thispresented disadvantages as consequently the hydropneumatic orhydromechanical accumulator (or the reserve of liquid with itsassociated elastic means for maintenance under pressure) had to beinstalled in or near the cutout chamber (FIGS. 1 and 3 of the aforesaidpatent), i.e., in the live part of the circuit-breaker, which isscarcely practical, or near the earth potential (FIG. 2 of the aforesaidpatent), but in this case with one conduit of ample section (moreparticularly through the insulating column of the circuit-breaker),which is uneconomical where high pressures are used.

In order to obviate or mitigate these disadvantages, the inventor soughtto avoid the use of elastic means for keeping under pressure thedielectric liquid for setting the movable contact in motion in thedirection separating the contacts. He arrived at this surprisingconclusion that, providing the volume of dielectric liquid is selectedto be sufficiently large and/or providing a liquid having a relativelylarge compressibility is selected as the dielectric liquid, thevolumetric elasticity of the dielectric liquid could simply be used asthe elastic disconnecting means.

Consequently the subject of the invention is a circuitbreaker whichincludes: a fluid-tight cutout chamber in which are disposed a fixedcontact as well as a sliding movable contact and which encloses adielectric in the liquid state kept under pressure; releasabledisconnecting means for bringing and keeping selectively the movablecontact against the fixed contact in opposition to ever-present elasticdisconnecting means tending to separate the movable contact from thefixed contact, said elastic disconnecting means being hydraulic elasticmeans responding only to the volumetric elasticity of the compresseddielectric liquid in the circuit-breaker.

It has heretofore been proposed to set in motion a movable contact of acircuit-breaker in the direction of opening this movable contact, underthe sole action of the natural elasticity of a dielectric under pressurecontained in the cutoff chamber of the circuit-breaker. However, such asolution has been proposed only for circuit-breakers in which the cutoffchamber is filled with a compressed gas having a high extinguishingpower, especially the gas SF 6. Such a solution would be usable inpractice only provided that the gas is maintained at a temperaturesufficiently high that its pressure, even when the external temperatureis very low, remains greater than an amount equal to the atmosphericpressure to ensure the effort necessary for disconnecting thecircuit-breaker. Because of this, circuitbreakers of this kind must befitted with an auxiliary heating system, and this presents disadvantagesfrom the safety aspect. Indeed, in case of trouble with the heatingsystem, the circuit-breaker could be unable to open if the externaltemperature is low, due to the fact of insufficient gas pressure in thecutoff chamber.

On the contrary, the circuit-breaker according to the invention callsexclusively on the volumetric elasticity of a dielectric in the liquidstate and not at all gaseous and of which the pressure remainssufficient, whatever may be the external temperature, to ensure thedisconnecting operation without necessitating auxiliary heating means.

The replacement according to the invention of a gaseous dielectric by adielectric liquid under pressure and particularly as will appearhereinafter, by a liquified dielectric gas of high compressibility,consequently achieves important and unexpected advantage from the aspectof simplicity of the construction and security of operation.

According to a preferred embodiment of the invention, the dielectricliquid is constituted by a liquified dielectric gas under pressure,especially sulphurhexafluoride SF 6 the dielectric properties of whichare very favourable and the compressibility of which is several tens oftimes greater than that of a liquid such as oil.

In a circuit-breaker according to the invention, as the elasticity ofthe dielectric itself is sufficient to take the place of elasticdisconnecting means hitherto utilised, the internal volume of thecircuit-breaker filled with dielectric liquid under pressure(particularly the cutoff chamber) could theoretically be sealed in afluid-tight manner. However, because of the variations in ambienttemperature, it is necessary to provide means for compensating forresultant variations in pressure of the dielectric.

This compensating means could advantageously be constituted by anaccumulator, for example a hydropneumatic accumulator, but the latterhas only to compensate for slow dilations, so that it could be connectedto the cutoff chamber simply by a conduit of crosssection as small astechnology allows and which may be of considerable length withoutdisadvantage. Consequently, the accumulator may be disposed at groundlevel, a fact which resolves the difficulties pointed out hereinbeforein connection with circuit-breakers of this kind hitherto known. It isthus possible to inspect and fill the accumulator at earth potentialwhich is much more economical and practical than when it is in the livepart of the circuit-breaker.

Finally, such conduits of small cross-section are much more practicaland economical for the high pressures utilised than are conduits oflarge cross-section which have hitherto been necessary.

The invention will be better understood with the help of the descriptionwhich follows, by way of example, with reference to the accompanyingdrawings, in which:

FIG. '1 is a diagrammatic sectional view of a circuitbreaker inaccordance with the invention; and

FIG. 2 is a partial view, on a larger scale, of the cutoff componentsaccording to a preferred form arising from a modification of theinvention.

The circuit-breaker, shown in FIG. 1 in the disconnected position,comprises essentially a cutoff chamber 2 constituted for example by acylindrical wall 4 closed in a fluid-tight manner by an upper wall 6 andby a bottom 8.

The cutoff chamber 2 encloses a fixed contact 10 and a sliding movablecontact 12. The fixed contact 10 is surrounded by a sleeve 14 ofinsulating material which is supported, by its upper annular surface 16,against the lower surface of the upper wall 6 of the cutoff chamber inorder to resist thrust exerted by the pressure of the dielectric and bythe movable contact on the fixed contact in the connected position ofthe circuitbreaker. The insulating sleeve 14 is extended by a tubularpart 18, the length of which is selected as a function of the voltageswhich the circuit-breaker will have to tolerate, and which surround'aconductive stem the upper end 22 of which constitutes one of thecircuitbreaker terminals connected to the line 24 to be cut.

The movable contact 12 passes in a fluid-tight manner, thanks to apacking ring 26 (preferably a resilient packing ring), through thebottom 8 of the cutoff chamber and includes abutment means limiting theextent of separation of the movable contact 12 from the fixed contact10. This abutment means is constituted by a shoulder 28 of the movablecontact, which shoulder comes to be supported, in the disconnected position, on the bottom 8 of the cutoff chamber.

The movable contact 12 is electrically connected to the second terminal30 of the circuit-breaker, the terminal 30 being itself connected to thebranch 24' of the line to be cut. As will hereinafter appear, the extentof movement of the movable contact, i.e., its maximum separation fromthe fixed contact may be greatly reduced (by comparison with thestandard circuitbreakers), so that the electrical connection between themovable contact and the terminal 30 may be effected simply by means of ametal braid 32, thus avoiding sliding contacts which are generallynecessary with circuit-breakers.

The cutoff chamber 2 forms a fluid-tight enclosure which is filled withdielectric liquid kept under pressure, the means keeping the liquidunder pressure being described hereinafter.

The dielectric liquid may be simply oil under pressure, but, in acircuit-breaker according to the invention, use is preferably made, forfilling the cutoff chamber, of a dielectric constituted by a dielectricgas liquified by pressure and maintained permanently in the liquidstate. There will hereinafter be pointed out the advantages which arederived from the use of such a dielectric.

The bottom 8 of the cutoff chamber is mounted on the top of aninsulating component, for example an insulating column 34 filled with aliquid or gaseous dielectric, for example oil or gaseous sulphurhexafluoride under low pressure, the lower end of the column being fixedon base-plate 36 mounted on a support 38 supported from the ground.

The movable contact 12 is mechanically connected, for example by aninsulating rod 40 extending in the interior of the column 34, toreleasable disconnecting means adapted to bring and keep selectively themovable contact against the fixed contact in opposition to ever-presentelastic disconnecting means which tend to separate the movable contactfrom the fixed contact.

The disconnecting means are standard in circuit breakers and it will besufficient to describe, by way of example, those represented in FIG. 1.

The lower extremity of the insulating rod 40 is connected, at leastunder thrust, to a piston 42 which slides in a jack cylinder 44 carriedby the base-plate 36, a fluid-tight packing ring 46 being providedbetween the piston and the cylinder.

The interlocking jack 44 may be actuated by a standard hydrauliccircuit-breaker control the essential parts of which have beenschematically represented at 48 and which does not form part of theinvention. These essential parts are an oleopneumatic accumulator 50, anoil-pump 52, a low-pressure oil reservoir 54, and a hydraulic switchingcircuit represented in a simplified manner by a three-way valve 56.

The fluid-tight cutoff chamber 2 could be provided with a simple orificeor valve for filling with dielectric under pressure series, as willhereinafter appear, the everavailable elastic disconnecting means areconstituted solely by the volumetric elasticity of the dielectric liquidcompressed in the cutoff chamber. That is to say that, supposing thecircuit-breaker is placed somewhere at constant temperature, it couldfunction with the mere essential components which have been described,after the cutoff chamber had been filled with dielectric liquid underpressure.

However, in order to compensate for large variations in temperature (forexample from 50C to +C) to which outside circuit-breakers could besubject, it is necessary to provide compensating means which at the sametime comprise filling and control means.

To this end, the cutoff chamber includes an orifice, for example apassage 58 pierced in the bottom 8 of the chamber, the passage 58 beingconnected with a pipe 60 of small cross-section located in the interiorof the insulating column 34. The pipe 60 (or a passage 62 connectedtherewith and pierced in the base-plate 36) issues at the potential ofthe ground where it is connected with a reserve of dielectric liquidunder pressure constituted for example by a hydropneumatic accumulator64 the liquid chamber 66 of which encloses a dielectric liquid underpressure and the gas chamber 68 of which encloses an elastic cushion ofcompressed gas such as nitrogen or preferably helium. A filling pipe 70,a pressure-gauge 72 and stop-valves 74, 76 and 78 are also provided.

When the accumulator 64 and the cutoff chamber 2 have first been filledwith dielectric liquid under pressure, the manner of operation of theapparatus is the following, starting out from the disconnected positionrepresented in FIG. 1. The movable contact 12, which forms aplungerpiston, is repulsed into its lowermost position by the pressureof the dielectric. For engagement of the circuit-breaker, the hydraulicengaging jack 44 is supplied, by actuating the switching means 56 sothat the piston 42 causes the movable contact 12 to move upwards,through the intermediary of the rod 40, until it is against the fixedcontact. As long as the jack 44 is supplied, generally by a hydrauliccircuit which is automatically sustained, the circuit-breaker remainsengaged. In order to effect disengagement of the circuit-breaker, thejack 44 is set to drainage in a standard manner and it is simply thevolumetric elasticity of the dielectric liquid under pressure containedin the cutoff chamber which drives away the movable contact andseparates it from the fixed contact, without any large flow of oildeveloping through the pipe 60 in the direction of the accumulator 64,so much so that, as long as the temperature is constant, the stop valve74 may be closed.

It is especially worth using as dielectric the liquified gas SF 6, forexample under a pressure of the order of 200 bars-to 400 bars (1 bar1.02 kg./cm

With such a dielectric, the separation of the contacts in the openposition may be greatly reduced, for example about mm. for a voltage of200 k/volts.

The volume of dielectric displaced by the movement of the movablecontact may thus be cm. Given that the compressibility of liquid SF 6 isvery high (about 10"" per kg./cm instead of 5 to 7 X 10 for oil), areduced volume (for example 4,000 cm) in the cutoff chamber issufficient in order that the variations in pressure (at constanttemperature) due to the displacement of the contact are low and of theorder of 5 bars.

The reserve of dielectric liquid constituted by the accumulator 64 maythus be remote from the cutoff chamber, the flow of liquid from theaccumulator 64 in the direction of the chamber 2, or vice versa, takingplace only slowly, as a function of variations in temperature.

The pressure gauge 72 enables the pressure of the dielectric to becontrolled.

In the case where oil under pressure would be used as the dielectric,the conditions would be less advantageous as oil is much lesscompressible than liquid SF 6 and necessitates greater separation of thecontacts, but it would suffice in this case to increase sufficiently thevolume of the cutoff chamber.

5 To achieve the greatest possible reduction in the movements of themovable contact, it is advantageous to use fixed and movable contactswithout preliminary engagement, that is to say contacts operating solelyunder pressure. That is why a hydraulic control of the kind representedin FIG. 1, with which the oil pressure applies the movable contact onthe fixed contact during periods when engagement is maintained, isparticularly advantageous.

A preferred modification in the construction of the movable contact isrepresented in FIG. 2.

According to this modification, the movable contact 12, instead offunctioning as a plunger-piston as in the case of FIG. 1, is connectedto a piston which slides in a cylinder 82 formed in the bottom 8 of thecutoff chamber. A packing ring 26 ensures fluid-tightness between thebottom 8 and the piston 80, a second packing ring 26" ensuring relativefluid-tightness between the shank of the movable contact and the bottom8.

The movable contact is pierced by an axial opening 84 which communicatesthrough transverse openings 86 with the chamber of the cylinder 82. Atthe instant of disengagement, the movable contact is repulsed by thevolumetric elasticity of the dielectric under pressure, as hashereinbefore been described. The displacement of the piston 80 increasesthe volume of the chamber 82 (FIG. 2) which fills with dielectric liquidwhich flows through the opening 84 and the openings 86 on passagebetween the opened fixed and movable contacts. In this way there isproduced a turbulent blowout of the are under the effect of thisdielectric flow. As the time of opening may be very brief, for example lto 2 milliseconds, the instantaneous flow may be very important.

One embodiment of a direct-current circuit-breaker sustaining arestoration voltage of 200 KV may have contacts of surface area about 10cm" and the applied force of the contact in the engaged position isabout 10 tons, representing the difference between the force of thehydraulic jack 44 and the force of the piston 80. The volume of SF 6delivered by the blowout is about 50 cm in l to 2 milliseconds.

Of course, the invention is in no way restricted to the embodimentdescribed and shown and is capable of many modifications, open to theexpert, in accordance with the contemplated applications, withoutthereby departing from the scope of the invention as defined in theappended claims.

I claim:

1. A circuit breaker comprising:

a circuit interrupting chamber enclosing an elastically compressible andpartially compressed dielectric liquid body;

a fixed contact member disposed in said liquid body;

a cylindrical contact member which is axially movable relative to thefixed contact member between a closed circuit position and an opencircuit position and having a portion thereof entering said liquid bodyso as to additionally compress the same during movement of the movablecontact member from said open circuit position to said closed circuitposition; releasable actuating means operable to move the movablecontact member from its open circuit position towards and maintain it inits closed circuit position against the sole action of the increasedcounterpressure created in said liquid body by said additionalcompression thereof, and means for releasing said actuating means andthereby allow said increased counterpressure to move the movable contactmember from its closed circuit position to its open circuit position. 2.A circuit-breaker according to claim 1, in which the dielectric in theliquid state is a compressible liquid having a compressibility at leastten times greater than that of oil.

3. A circuit-breaker according to claim 2, in which the dielectric inthe liquid state is a liquified gas dielectric.

. 4. A circuit-breaker according to claim 3, in which the dielectricunder pressure is sulphur hexafluoride SF 6 under pressure.

5. A circuit-breaker according to claim 1 and including means forcompensating for variations in volume of the dielectric liquid caused byvariations in temperature.

6. A circuit-breaker according to claim 5, in which the compensatingmeans comprise a fluid-tight enclosure containing dielectric in theliquid state, pneumatic or mechanical elastic means acting on saiddielectric liquid to maintain the dielectric liquid under pressure, anda conduit of small cross-section communicating between said enclosureand the cutoff chamber of the circuit-breaker, said conduit permittingonly small flows of liquid caused by variations in the volume of liquiddue to variations in temperature.

7. A circuit-breaker according to claim 6, in which said compensatingmeans comprise a hydropneumatic accumulator inflated by helium.

8. A circuit-breaker according to claim 1, in which the movable contactis connected to a disconnecting piston which slides in a cylinder theworking chamber of which communicates with the cutoff chamber filledwith dielectric liquid under pressure, such communication being by wayof an opening pierced at least in part axially in the movable contactand thanks to which a movement of dielectric across the movable contactis established when the latter is displaced, said movement producing aflow of dielectric liquid in the zone where the cutoff arc is formed atthe instant when the circuitbreaker is opened.

9. A circuit-breaker according to claim 8, in which, in the engagedposition of the circuit-breaker, the movable contact is supportedagainst the fixed contact without engagement of one contact within theother.

10. A circuit-breaker according to claim 9, in which the releasableengaging means to bring and selectively maintain the movable contactagainst the fixed contact in opposition to the elastic pressure of thedielectric liquid under pressure comprises at least one hydraulicengaging jack moving the movable contact, and control means forsupplying and draining said hydraulic jack.

1. A circuit breaker comprising: a circuit interrupting chamber enclosing an elastically compressible and partially compressed dielectric liquid body; a fixed contact member disposed in said liquid body; a cylindrical contact member which is axially movable relative to the fixed contact member between a closed circuit position and an open circuit position and having a portion thereof entering said liquid body so as to additionally compress the same during movement of the movable contact member from said open circuit position to said closed circuit position; releasable actuating means operable to move the movable contact member from its open circuit position towards and maintain it in its closed circuit position against the sole action of the increased counterpressure created in said liquid body by said additional compression thereof, and means for releasing said actuating means and thereby allow said increased counterpressure to move the movable contact member from its closed circuit position to its open circuit position.
 2. A circuit-breaker according to claim 1, in which the dielectric in the liquid state is a compressible liquid having a compressibility at least ten times greater than that of oil.
 3. A circuit-breaker according to claim 2, in which the dielectric in the liquid state is a liquified gas dielectric.
 4. A circuit-breaker according to claim 3, in which the dielectric under pressure is sulphur hexafluoride SF 6 under pressure.
 5. A circuit-breaker according to claim 1 and including means for compensating for variations in volume of the dielectric liquid caused by variations in temperature.
 6. A circuit-breaker according to claim 5, in which the compensating means comprise a fluid-tight enclosure containing dielectric in the liquid state, pneumatic or mechanical elastic means acting on said dielectric liquid to maintain the dielectric liquid under pressure, and a conduit of small cross-section communicating between said enclosure and the cutoff chamber of the circuit-breaker, said conduit permitting only small flows of liquid caused by variations in the volume of liquid due to variations in temperature.
 7. A circuit-breaker according to claim 6, in which said compensating means comprise a hydropneumatic accumulator inflated by helium.
 8. A circuit-breaker according to claim 1, in which the movable contact is connected to a disconnecting piston which slides in a cylinder the working chamber of which communicates with the cutoff chamber filled with dielectric liquid under pressure, such communication being by way of an opening pierced at least in part axially in the movable contact and thanks to which a movement of dielectric across the movable contact is established when the latter is displaced, said movement producing a flow of dielectric liquid in the zone where the cutoff arc is formed at the instant when the circuit-breaker is opened.
 9. A circuit-breaker according to claim 8, in which, in the engaged position of the circuit-breaker, the movable contact is supported against the fixed contact without engagement of one contact within the other.
 10. A circuit-breaker according to claim 9, in which the releasable engaging means to bring and selectively maintain the movable contact against the fixed contact in opposition to the elastic pressure of the dielectric liquid under pressure comprises at least one hydraulic engaging jack moving the movable contact, and control means for supplying and draining said hydraulic jack. 